This invention relates to a diffusion-type light head for use as a part of a photographic enlarger for the making of photographic prints. More specifically, it utilizes interchangeable light mixing chambers and a light source positioning means adapted to maintain the light source close to the negative or mixing chamber to maximize the light flux through the negative by reducing the length of the optical path, yet obtain optimum light mixing and achieve relatively uniform flux at all exit locations.
Diffusion light heads and light mixing chambers, particularly suited for use with photographic enlargers and projection devices, are known in the art. A white light source, i.e. one emitting a full spectrum of colors, is mounted at one focal point of an ellipsoidal reflector. A number of color correction filters are mounted between the first and second focal points of the reflector for selective partial interference with the light beam to adjust its chromaticity as necessary to provide the desired print. A mixing chamber is disposed with an inlet at the second focal point of the reflector to accept the color corrected light. Because color correction is accomplished by selected partial insertion of one or more filters into the white light, only portions of the beam are colored, and the colored portions have a lower flux (luminous energy per unit area) due to the reflection or absorption of light by the colored filters. Thus, a mixing chamber is used to scramble the light admitted thereinto to provide a homogeneous color light beam of uniform flux at the exit port. A negative or other transparency is usually placed immediately adjacent the exit port to create an image for printing or projection.
It is desireable to maximize the amount of light flux incident upon a negative in order to decrease printing times. This reduces labor costs, maximizes the efficiency of the enlarging equipment, and reduces the "on" time of the enlarger lamp. In the past, this has been accomplished by utilizing interchangeable light mixing chambers, each having exit ports sized to accommodate a transparency of a given size. Light flux was thus increased by reducing the area over which the light was spread. An example of an enlarger utilizing different size interchangeable light mixing chambers and a fixed light source is Weisglass U.S. Pat. No. 3,684,371, commonly owned with the subject application. However, as recognized by the laws of physics, the intensity of the light varies inversely as the square of the distance from the source. And, merely reducing the area of the exit port of the mixing chamber without lessening the distance from the light source to the negative does not increase the light intensity at the exit port.